Polarization conversion systems for stereoscopic projection

ABSTRACT

A polarization conversion system (PCS) is located in the output light path of a projector. The PCS may include a polarizing beam splitter, a polarization rotating element, a reflecting element, and a polarization switch. Typically, a projector outputs randomly-polarized light. This light is input to the PCS, in which the PCS separates p-polarized light and s-polarized light at the polarizing beam splitter. P-polarized light is directed toward the polarization switch on a first path. The s-polarized light is passed on a second path through the polarization rotating element (e.g., a half-wave plate), thereby transforming it to p-polarized light. A reflecting element directs the transformed polarized light (now p-polarized) along the second path toward the polarization switch. The first and second light paths are ultimately directed toward a projection screen to collectively form a brighter screen image in cinematic applications utilizing polarized light for three-dimensional viewing.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation application of and claimspriority to U.S. patent application Ser. No. 13/047,763, entitled“Polarization conversion systems for stereoscopic projection,” filedMar. 14, 2011 that is a continuation application of U.S. patentapplication Ser. No. 11/864,198 entitled “Polarization conversionsystems for stereoscopic projection,” filed Sep. 28, 2007, now U.S. Pat.No. 7,905,602 which relates and claims benefit of: (a) U.S. provisionalpatent application No. 60/827,657, entitled “Polarization ConversionSystem for Cinematic Projection,” filed Sep. 29, 2006; (b) U.S.provisional patent application No. 60/911,043, entitled “Polarizationconversion system for 3-D projection,” filed Apr. 10, 2007; and (c)provisional patent application No. 60/950,652, entitled “Polarizationconversion system for 3-D projection,” filed Jul. 19, 2007. Allapplications referenced above are incorporated by reference.

TECHNICAL FIELD

This disclosure relates to a projection system for projecting images fora three-dimensional viewing experience, and more in particular to apolarization conversion system utilizing polarized light for encodingstereoscopic images.

BACKGROUND

Three-dimensional (3D) imagery can be synthesized using polarizationcontrol following the projector and polarization controlling eyewear(see, e.g., U.S. Pat. No. 4,792,850 to Lipton, which is herebyincorporated by reference herein).

A conventional implementation of polarization control at the projectoris shown in FIG. 1. In this implementation, nearly parallel rays emergefrom the output of the lens 10, appearing to originate from a pupil 12inside of the lens 10, and converge to form spots on a screen 14. Raybundles A, B, and C in FIG. 1 are bundles forming spots at the bottom,center, and top of a screen 14, respectively. The light 20 emerging fromthe projection lens is randomly polarized, depicted in FIG. 1 as both s-and p-polarized light [s-polarized light is conventionally representedas ‘o’; p-polarized light is represented with a double arrow-endedline]. The light 20 passes through a linear polarizer 22, resulting in asingle polarization state after the polarizer 22. The orthogonalpolarization state is absorbed (or reflected), and the light flux afterthe polarizer 22 is typically less than half of the original flux, thusresulting in a dimmer final image. The polarization switch 30 issynchronized with the image frame, and the polarization state 24emerging from the polarization switch is alternated, producing images ofalternately orthogonal polarization at the screen.Polarization-selective eyewear allows images of one polarization to passto the left eye, and images of the orthogonal polarization to pass tothe right eye. By presenting different images to each eye, 3D imagerycan be synthesized.

This conventional system has been used in theatres. However, theconventional system requires that greater than 50% of the light isabsorbed by the polarizer, and the resulting image is greater than 50%dimmer than that of a typical 2D theatre. The dimmer image can limit thesize of theatre used for 3D applications and/or provides a lessdesirable viewing experience for the audience.

SUMMARY

Addressing the aforementioned problems, various embodiments ofpolarization conversion systems that receive light from a projector aredescribed. The polarization conversion systems present a brighter screenimage in cinematic applications utilizing polarized light forthree-dimensional viewing.

In an embodiment, a polarization conversion system includes apolarization beam splitter (PBS), a polarization rotator, and apolarization switch. The PBS is operable to receive randomly-polarizedlight bundles from a projector lens, and direct first light bundleshaving a first state of polarization (SOP) along a first light path. ThePBS is also operable to direct second light bundles having a second SOPalong a second light path. The polarization rotator is located on thesecond light path, and is operable to translate the second SOP to thefirst SOP. The polarization switch is operable to receive first andsecond light bundles from the first and second light paths respectively,and to selectively translate the polarization states of the first andsecond light bundles to one of a first output SOP and a second outputSOP. First light bundles are transmitted toward a projection screen. Areflecting element may be located in the second light path to directsecond light bundles toward a projection screen such that the first andsecond light bundles substantially overlap to form a brighter screenimage.

In accordance with another aspect of the disclosure, a method forstereoscopic image projection includes receiving randomly-polarizedlight from a projector, directing first state of polarization (SOP)light on a first light path, and directing second SOP light on a secondlight path. The method also includes transforming the second SOP lighton the second light path to first SOP light, and selectively translatingthe first SOP light on both light paths to one of a first output SOP anda second output SOP.

Other aspects and embodiments are described below in the detaileddescription.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a conventional polarization switch forstereoscopic projection;

FIG. 2 is a schematic diagram of a polarization conversion system (PCS)for cinematic projection in accordance with the present disclosure;

FIG. 3 is a schematic diagram of another embodiment of a PCS forcinematic projection in accordance with the present disclosure;

FIG. 4 is a schematic diagram of another embodiment of a PCS forcinematic projection, including a telephoto lens along an optical pathand with the field of view centered on the optical axis, in accordancewith the present disclosure;

FIG. 5 is a schematic diagram of another embodiment of a PCS forcinematic projection, including a telephoto lens along an optical pathand with the field of view not centered on the optical axis, inaccordance with the present disclosure;

FIG. 6 is a schematic diagram of another embodiment of a PCS forcinematic projection to provide a circularly-polarized output, includinga telephoto lens along an optical path and with field of view centeredon an optical axis, in accordance with the present disclosure;

FIG. 7 is a schematic diagram of another embodiment of a PCS forcinematic projection to provide a linearly-polarized output, including atelephoto lens along an optical path and with field of view centered onan optical axis, in accordance with the present disclosure; and

FIG. 8 is a schematic diagram of another embodiment of a PCS forcinematic projection in accordance with the present disclosure.

DESCRIPTION

Various embodiments of polarization conversion systems that receivelight from a projector are described. The polarization conversionsystems present a brighter screen image in cinematic applicationsutilizing polarized light for three-dimensional viewing.

FIG. 2 is a schematic diagram showing a polarization conversion system(PCS) 100 for cinematic projection. An embodiment of the polarizationconversion system 100 includes a polarizing beam splitter (PBS) 112, apolarization rotator 114 (e.g., a half-wave plate), a relecting element116 (e.g., a fold mirror), and a polarization switch 120, arranged asshown. The polarization conversion system 100 may receive images from aconventional projector with a projection lens 122.

In operation, ray bundles A, B, and C emerge randomly polarized from thelens 122 and are projected toward a screen 130 to form an image. In thisembodiment, a PBS 112 is inserted in place of the polarizer 22 shown inFIG. 1. The PBS 112 transmits P-polarized light 124, and reflectsS-polarized light 126. The P-polarized light 124 passes through thepolarization switch (bundles A, B, and C) and is rotated by thepolarization switch in alternating frames, same as bundles A, B, and Cin FIG. 1.

The S-polarized light 126 reflected by the PBS 112 passes through apolarization rotator 114 (e.g., a half-wave plate, preferably achromaticin some embodiments) and is rotated to p-polarized light 128. The newp-polarized light 128 passes to a fold mirror 116. The fold mirror 116reflects the new p-polarized light 128 and passes it to polarizationswitch 120. The polarization switch 120, acting on p-polarized raybundles A′, B′, and C′, rotates the polarization of the ray bundles inalternating frames, in synchronization with the rotation of bundles A,B, and C. The position of bundles A′, B′, and C′ at the screen may beadjusted (e.g., by adjusting the tilt of the fold mirror 116) to closelyor exactly coincide with the positions of bundles A, B, and C at thescreen. Since nearly all of the randomly polarized light 106 from theprojection lens 122 is imaged at the screen 130 with a singlepolarization state, the resulting image of the system in FIG. 2 isapproximately two times brighter than the image at the screen for thesystem in FIG. 1.

In this exemplary embodiment, the PBS 112 in FIG. 2 is depicted as aplate. However, various types of PBSs may be used. For example, the PBSplate may be constructed using a wire grid layer on glass (e.g., Profluxpolarizer from Moxtek in Orem, Utah), polarization recycling film (e.g.,Double Brightness Enhancing Film from 3M in St. Paul, Minn.),polarization recycling film on glass (for flatness), or amulti-dielectric layer on glass. The PBS 112 in FIG. 2 couldalternatively be implemented as a glass cube (with wire grid,polarization recycling film, or dielectric layers along the diagonal) toreduce astigmatism in the final image associated with light passingthrough a tilted plate. Alternatively, the tilted plate PBS 112 in FIG.2 may, in various embodiments, be implemented with spherical, aspheric,cylindrical or toroidal surfaces to reduce astigmatism in the finalimage at the screen 130. De-centered spherical, aspheric, cylindrical ortoroidal surfaces on the plate, and/or additional de-centered spherical,aspheric, cylindrical or toroidal elements in the optical path after theplate can be implemented to reduce astigmatism in the final image. See,e.g., “Simple method of correcting the aberrations of a beamsplitter inconverging light,” V. Doherty and D. Shafer, Proc. SPIE, Vol. 0237, pp.195-200, 1980, which is hereby incorporated by reference. It should alsobe noted that a second flat plate may be inserted into the system afterthe tilted PBS plate 112 and its tilt adjusted to reduce or correctastigmatism in the final image.

In some embodiments, the polarization rotator 114 in FIG. 2 may be anachromatic half-wave plate. The half-wave plate may be implemented withpolymer films (e.g., Achromatic Retardation Plate from ColorLink, Inc.,Boulder, Colo.), quartz plates, or a static liquid crystal deviceoptionally patterned to account for geometric polarization alteration.The half-wave plate 114 may be positioned as shown in FIG. 2, or inother embodiments, it may be positioned between the fold mirror 116 andpolarization switch 120, intersecting ray bundles A′, B′, and C′. Thisimplementation may be desirable, as bundles A′, B′, and C′ reflect fromthe fold mirror 116 in s-polarization state and mirrors often have ahigher reflection for s-polarized light. However, with such animplementation, the half-wave plate 114 should be located such thatbundles A′ and C do not overlap at the plate. Although in most describedembodiments herein, the polarization rotator 114 is located in thesecond light path, it may alternatively be placed in the first lightpath instead, and the polarization conversion system will operate in asimilar manner in accordance with the principles of the presentdisclosure.

In some embodiments, the fold mirror 116 may be replaced with a PBSelement (e.g., wire grid plate). In this case, a purer polarization maybe maintained after the PBS element.

Polarization switch 120 may be a switch as taught by U.S. Pat. No.4,792,850; a switch as taught by any of the switches ofcommonly-assigned U.S. patent application Ser. No. 11/424,087 entitled“Achromatic Polarization Switches”, filed Jun. 14, 2006; both of whichare incorporated by reference in their entirety for all purposes, or anyother polarization switch known in the art that selectively transformsan incoming state of polarization. In some embodiments, the polarizationswitch 120 can be split (i.e., to increase yield of the device). If thepolarization switch 120 is split, it is desirable that the two devicesare located such that there is no overlap of bundles A′ and C in FIG. 2.Splitting the polarization switch 120 allows one portion to be relocatedin the A′, B′, C′ optical path between the half-wave plate 114 and foldmirror 116. Placing the polarization switch 120 here may call for thefold mirror 116 to have better polarization preserving properties (e.g.,a Silflex coating from Oerlikon in Golden, Colo.) as this may be thelast element in the A′, B′, C′ optical path prior to the screen.

In the polarization conversion system 100 of FIG. 2, the optical path ofray bundle A′ is longer than that of ray bundle A (similarly B′−B andC′−C) resulting in a magnification difference between the imagesproduced by A′, B′, C′ and A, B, C. This magnification difference may beunacceptable to an audience, especially for wide angle and short-throwprojection systems. Some techniques for correcting this magnificationdifference may include (1) providing a curved surface on the fold mirror116 with optical power that compensates for the magnificationdifference; this solution is achromatic, which is desirable; (2) addinga fresnel or diffractive surface with optical power to the fold mirror116 to compensate for the magnification difference (which may or may notbe achromatic); (3) adding a refractive element (lens) between the foldmirror 116 and polarization switch 120, or between the PBS 112 and foldmirror 116; a singlet lens is unlikely to be achromatic, but a doubletsolution can be achromatic; (4) addition of a telephoto lens asillustrated in FIGS. 3 and 4; or (5) a combination of at least two ofthe above four techniques.

Although as described, p-polarized light is transmitted toward thepolarization switch 120, while s-polarized light is directed towardhalf-wave plate 114, it should be apparent to a person of ordinary skillin the art that an alternative configuration may be employed in whichs-polarized light is transmitted toward the polarization switch 120,while p-polarized light is directed toward the half-wave plate 114.

FIG. 3 is a schematic diagram showing another embodiment of a PCS forcinematic projection 200. The elements of PCS 200 may be of similar typeand function for those shown with respect to PCS 100 of FIG. 2. Forinstance, elements 2 xx are similar to elements 1 xx, where xx are thelast two digits of the respective elements. In this embodiment, raybundles A, B, and C may be directed through an additional set of foldmirrors 232, 234 operable to equalize the optical path lengths ofbundles A and A′, B and B′, C and C′ as shown in FIG. 3. [Note: bundlesA′ and C′ are present, but not illustrated. They follow a similar pathto the A′, B′, C′ bundles shown in FIG. 2]. Note that although the PBSand fold mirrors are shown here to be orientated at 45 degrees to theoptical axis, the PBS 212 and fold mirrors 216, 232, 236 may have otherorientations in accordance with the present teachings. Additionally,glass may be inserted into the optical path of A′, B′, and C′ (e.g., byreplacing the fold mirror 216 with a right angle prism and/or using aglass cube PBS in place of a plate PBS) to reduce or eliminate theoptical path difference between the A, B, C and A′, B′, C′ bundles,respectively.

With reference to FIGS. 2 and 3, the image from bundles A′, B′, and C′should substantially overlap the image from bundles A, B, and C forviewing comfort (although perfect overlap is not necessarily required).Some techniques of adjusting one image location relative to the otherinclude (1) using thumb screws or a similar mechanical techniques totilt the fold mirror, PBS plate, or PBS cube; (2) mechanicallyde-centering a lens or element with optical power (e.g. curved mirror);(3) utilizing a feedback system to automatically adjust image positionvia one of the aforementioned image adjustment techniques; or (4) acombination of at least two of the above three techniques.

Optical transmission and stray light control may be optimized onoptically transmissive elements by providing an anti-reflection coatthereon for high transmission and low reflection. Reflections fromtransmissive elements can cause stray light in the system which degradescontrast and/or produces disturbing artifacts in the final image. Insome embodiments, additional absorptive polarizers may be placed afterthe half-wave plate 114 in the A′, B′, C′ path and/or after the PBS 112in either path to control polarization leakage and improve the finalimage contrast.

FIG. 4 is a schematic diagram showing another embodiment of a PCS forcinematic projection 300. The elements of PCS 300 may be of similar typeand function for those shown with respect to PCS 100 of FIG. 2. Forinstance, elements 3 xx are similar to elements 1 xx, where xx are thelast two digits of the respective elements.

In this exemplary embodiment, a telephoto lens pair 340 may beimplemented in the optical path where light transmits through the PBS312. Here, telephoto lens pair 340 is located along an optical path andwith the field of view centered on the optical axis. Typically,telephoto lens 340 allows control of magnification, distortion, andimaging properties with two elements such that the two images overlayrelatively close, i.e., within 1-4 pixels of each other, whilemaintaining spots sizes on the order of a fraction of a pixel andlateral color on the order of a pixel. Alternatively, a reversetelephoto lens (not shown) may be implemented in the optical path wherelight reflects from the PBS 312 (located between the polarization switch320 and fold mirror 316, or after the fold mirror 316). If a telephotoor reverse telephoto lens is used for controlling magnification in oneoptical path, the radial distortion and keystone distortion of the finalimage can be tuned by laterally displacing the individual elements orpair of elements from the optical axis.

FIG. 5 is a schematic diagram showing another embodiment of a PCS forcinematic projection 400. The elements of PCS 400 may be of similar typeand function for those shown with respect to PCS 100 of FIG. 2. Forinstance, elements 4 xx are similar to elements 1 xx, where xx are thelast two digits of the respective elements. In this exemplaryembodiment, a telephoto lens pair 440 may be implemented in the opticalpath where light transmits through the PBS 412. Here, telephoto lenspair 440 is located along an optical path and with the field of viewdecentralized from the optical axis. Just as described above, the radialdistortion and keystone distortion of the final image can be tuned bylaterally displacing the individual elements or pair of elements 440from the optical axis.

FIG. 6 is a schematic diagram of another embodiment of a PCS forcinematic projection 500 that provides a circularly polarized output.PCS 500 includes a telephoto lens pair 540 along an optical path, withfield of view centered on an optical axis. In this case, eachpolarization switch 520 is a circular polarization switch (or Z-screen),e.g., as described in U.S. Pat. No. 4,792,850. The cleanup polarizers542, 544 in each path are optional, depending on the level of contrastdesired from the system. For example, including one or both cleanuppolarizers may enhance the system contrast.

FIG. 7 is a schematic diagram of another embodiment of a PCS forcinematic projection 600 that provides a linearly polarized output.Here, each polarization switch 620 is an achromatic linear polarizationswitch, as described in U.S. patent application Ser. No. 11/424,087entitled “Achromatic Polarization Switches”, filed Jun. 14, 2006; alsomanufactured by ColorLink, Inc., of Boulder, Colo. Similar to theexample in FIG. 6, cleanup polarizers 642, 644 in each path areoptional, depending on the level of contrast desired from the system.For example, including one or both cleanup polarizers may enhance thesystem contrast. Additionally, the achromatic rotator 648 is optional,depending on the achromatic properties of the polarization switch 620.

FIG. 8 is a schematic diagram of another embodiment of a PCS forcinematic projection 700, showing an alternative configuration in whichthe polarizers 746, achromatic rotator 714, and polarization switches720 are located after other optical components. The elements of PCS 700may be of similar type and function for those shown with respect to PCS100 of FIG. 2. For instance, elements 7 xx are similar to elements 1 xx,where xx are the last two digits of the respective elements.

In operation, light exits projection lens 722 toward PBS 712.P-polarized light passes through PBS 712 toward telephoto lens pair 740,then toward polarization switch 720. An optional cleanup polarizer 746may be located between telephoto lens pair 740 and polarization switch720 to further enhance contrast. The s-polarized light reflected by PBS712 is directed toward fold mirror 716, where it reflects toward anachromatic rotator 714 that transforms the s-polarized light intop-polarized light, then it passes through an optional cleanup polarizer746. Next, the p-polarized light from achromatic rotator 714 passesthrough polarization switch 720. In this configuration, the s-polarizedlight reflected by the PBS 716 is efficiently reflected, withpolarization maintained by the fold mirror 716. This relaxes any wantfor polarization preservation from the fold path and maximizesbrightness. An achromatic 90° rotator 714 (probably retarder stackbased) can be used to convert light from the fold mirror to theorthogonal state. In order to eliminate P-reflection from the PBS 712, aclean up polarizer 746 is likely desirable. This preferably follows theachromatic rotator 714, thereby reducing polarization conversionefficiency as a factor in system level contrast.

PCS 700 provides a high contrast image on the screen. In this exemplaryembodiment, the final screen image has a center located on the opticalaxis of the projection lens. In some other embodiments, the final screenimage may be located off-center from the optical axis—for example, ahalf screen height below the optical axis of the projection lens. Insuch embodiments, the polarizing beamsplitter 712 may be relocated tointercept the full illumination from the projection lens 722, and thefold mirror 716 may be tilted to properly overlay the two images on thescreen. The polarization switch 720 in this embodiment has been splitinto two elements (one for each path) to increase fabrication yield;although, as previously discussed, it could alternatively be a singleunit.

As used herein, the term “cinematic projection” refers to the projectionof images using front and/or rear projection techniques, and includes,but is not limited to, applications for cinema, home theatre,simulators, instrumentation, head-up displays, and other projectionenvironments where stereoscopic images are displayed.

While several embodiments and variations of polarization conversionsystems for stereoscopic projection have been described above, it shouldbe understood that they have been presented by way of example only, andnot limitation. Thus, the breadth and scope of the invention(s) shouldnot be limited by any of the above-described exemplary embodiments, butshould be defined only in accordance with any claims and theirequivalents issuing from this disclosure. Furthermore, the aboveadvantages and features are provided in described embodiments, but shallnot limit the application of such issued claims to processes andstructures accomplishing any or all of the above advantages.

Additionally, the section headings herein are provided for consistencywith the suggestions under 37 CFR 1.77 or otherwise to provideorganizational cues. These headings shall not limit or characterize theinvention(s) set out in any claims that may issue from this disclosure.Specifically and by way of example, although the headings refer to a“Technical Field,” such claims should not be limited by the languagechosen under this heading to describe the so-called technical field.Further, a description of a technology in the “Background” is not to beconstrued as an admission that technology is prior art to anyinvention(s) in this disclosure. Neither is the “Brief Summary” to beconsidered as a characterization of the invention(s) set forth in issuedclaims. Furthermore, any reference in this disclosure to “invention” inthe singular should not be used to argue that there is only a singlepoint of novelty in this disclosure. Multiple inventions may be setforth according to the limitations of the multiple claims issuing fromthis disclosure, and such claims accordingly define the invention(s),and their equivalents, that are protected thereby. In all instances, thescope of such claims shall be considered on their own merits in light ofthis disclosure, but should not be constrained by the headings set forthherein.

What is claimed is:
 1. A polarization conversion system comprising: apolarization beam splitter (PBS) operable to receive randomly-polarizedlight bundles from a projector lens, and direct first light bundleshaving a first state of polarization (SOP) along a first light path, anddirect second light bundles having a second SOP along a second lightpath; a polarization rotator located on the first light path, thepolarization rotator being operable to translate the second SOP to thefirst SOP; and a polarization switch operable to receive first andsecond light bundles from the first and second light paths respectively,and to selectively translate the polarization states of the first andsecond light bundles to one of a first output SOP and a second outputSOP; and wherein the polarization switch comprises first and secondpolarization switch panels, the first polarization switch panelreceiving light from the first light path, and the second polarizationswitch panel receiving light from the second light path.
 2. Thepolarization conversion system of claim 1, further comprising areflector located on the second light path, operable to direct secondlight bundles to substantially similar locations on a projection screenas the first light bundles.
 3. The polarization conversion system ofclaim 1, further comprising a telephoto lens pair located on the firstlight path, after the first polarization switch.
 4. The polarizationconversion system of claim 3, wherein the telephoto lens pair comprisesa positive lens and a negative lens separated by air.
 5. Thepolarization conversion system of claim 3, wherein the telephoto lenspair is an afocal converter.
 6. The polarization conversion system ofclaim 1, wherein the first output SOP is orthogonal to the second outputSOP.
 7. The polarization conversion system of claim 1, furthercomprising a pair of mirrors located on the first light path after thepolarization switch, the pair of mirrors being operable to substantiallyequalize the optical path length between the first light path and thesecond light path.
 8. The polarization conversion system of claim 1,wherein the polarization switch selects between the first and the secondoutput SOP in synchronization with transmission of an image frame by aprojector.
 9. The polarization conversion system of claim 1, wherein thepolarization rotator comprises a retarder stack.
 10. The polarizationconversion system of claim 1, wherein the polarization beam splitterincludes a wire grid layer.
 11. The polarization conversion system ofclaim 1, wherein the polarization beam splitter includes amulti-dielectric layer.
 12. A projection system utilizing polarizedlight for encoding stereoscopic images, comprising: a projectorcomprising a projection lens operable to output randomly-polarizedlight; a polarization conversion system optically coupled to theprojection lens, comprising: a polarization beam splitter operable todirect light on first and second light paths; a polarization rotationelement located on the first light path; a reflector element located onthe second light path; and a polarization switch located on the firstlight path and on the second light path before the reflecting element,wherein the first light path forms an image on a projection screen, andwherein the reflector element directs light on the second light pathtoward the projection screen.
 13. The polarization conversion system ofclaim 12, wherein the polarization beam splitter includes a wire gridlayer.
 14. The polarization conversion system of claim 12, wherein thepolarization beam splitter includes a multi-dielectric layer.
 15. Amethod for stereoscopic image projection, comprising: receivingrandomly-polarized light from a projector, the randomly-polarized lightbundles comprising stereoscopic imagery; directing first state ofpolarization (SOP) light on a first light path; directing second SOPlight on a second light path; transforming the second SOP light on thesecond light path to first SOP light; selectively translating the firstSOP light on both light paths to one of a first output SOP and a secondoutput SOP.
 16. The method for stereoscopic image projection of claim15, further comprising the step of directing the first and second lightpaths toward a projection screen.
 17. The method for stereoscopic imageprojection of claim 15, further comprising synchronizing the firstoutput SOP and second output SOP with transmission of an image framefrom the projector.
 18. A polarization conversion system comprising: apolarization beam splitter (PBS) operable to receive randomly-polarizedlight bundles from a projector lens, the randomly-polarized lightbundles comprising stereoscopic imagery, and direct first light bundleshaving a first state of polarization (SOP) along a first light path, anddirect second light bundles having a second SOP along a second lightpath; a polarization rotator located on the second light path, thepolarization rotator being operable to translate the second SOP to thefirst SOP; and a polarization switch operable to receive first andsecond light bundles from the first and second light paths respectively,and to selectively translate the polarization states of the first andsecond light bundles to one of a first output SOP and a second outputSOP.
 19. The polarization conversion system of claim 18, wherein thepolarization beam splitter includes a wire grid layer.
 20. Thepolarization conversion system of claim 18, wherein the polarizationbeam splitter includes a multi-dielectric layer.
 21. The polarizationconversion system of claim 18, further comprising a reflector located onthe second light path, operable to direct second light bundles tosubstantially similar locations on a projection screen as the firstlight bundles.
 22. The polarization conversion system of claim 18,wherein the polarization switch comprises a single panel that receiveslight from the first light path and the second light path.
 23. Thepolarization conversion system of claim 18, wherein the polarizationswitch comprises first and second polarization switch panels, the firstpolarization switch panel receiving light from the first light path, andthe second polarization switch panel receiving light from the secondlight path.
 24. The polarization conversion system of claim 18, furthercomprising a telephoto lens pair located on the first light path, afterthe first polarization switch.